Annular clutch plates used in fluid filled automatic transmissions are well known. A plurality of annular plates, each plate carrying at least one friction lining, are compressed together to transfer torque between independent members of the transmission. The torque transfer efficiency is improved by the lining, but improvements in the linings have been developed to address certain problems during engagement and release of the clutch plates with respect to each other.
One previously known type of wet multi-plate clutch includes a plurality of clutch plates, each plate having discrete separated segments of friction lining. The separations between the segments form oil passages from the radially inner edge to the radially outer edge of the clutch plate to permit the passage of fluid for lubrication and cooling. The segments also include oil retaining grooves that maintain an oil volume between mating friction linings to prevent sticking when the clutch plates are to be disengaged from each other.
Another known form of friction disc for use in multi-plate friction clutch packs includes annular core plate segmented with interlocking ends to form a ring. The ring includes friction facings which are also segmented and bonded to the core plate with facing segments overlapping the interlocking ends of the core plate segments. The ends of the friction facing segments may be interlocked or slightly spaced apart to form oil channels, while openings in the core pieces intersect circumferentially offset radial channels in the lining. The channels open only to either radially outer or radially inner edges of the friction segment so that the limited channels are coupled by core openings that pass through the disc.
Another known clutch disc includes molded annular clutch facing having a plurality of surface grooves molded into the facing. The grooves extend not substantially more than halfway across the annulus, and each groove is not greater than forty percent of the thickness of the facing in depth. The grooving improves torque capacity and hill start capability, provides reduced propensity for judder, improves take-up characteristics, and resists ringing-on, the phenomena that involves a facing adhering to a mating clutch plate surface and preventing the clutch from becoming disengaged.
Another improvement to disengage clutch plates includes a facing with a plurality of grooves that provide non-rectangular transitional areas together with grooves that provide rectangular transitional areas interposed therebetween.
While none of the above improvements are particularly concerned with the problem of reducing drag in a fluid environment, U.S. Pat. No. 5,134,005 provides a ring that has a plurality of fluid reservoirs in a groove extending between the reservoir and the outer periphery of the ring. In the patented structure, the area of the reservoir and the grooves is between five percent to ten percent of the total frictional surface area of the ring to reduce drag. However, as with other previously known clutch facing modifications, the formation of particularly configured grooves can substantially increase the cost of assembling and fabricating the components of the clutch plate.